Heart disease and stroke remain among the leading causes of death nationally. We examined whether differences in recent trends in heart disease, stroke, and total mortality exist in the United States and Kaiser Permanente Northern California (KPNC), a large integrated healthcare delivery system. The main outcome measures were comparisons of US and KPNC total, age-specific, and sex-specific changes from 2000 to 2015 in mortality rates from heart disease, coronary heart disease, stroke, and all causes. The Centers for Disease Control and Prevention Wide-Ranging Online Data for Epidemiologic Research data system was used to determine US mortality rates. Mortality rates for KPNC were determined from health system, Social Security vital status, and state death certificate databases. Declines in age-adjusted mortality rates were noted in KPNC and the United States for heart disease (36.3% in KPNC vs 34.6% in the United States), coronary heart disease (51.0% vs 47.9%), stroke (45.5% vs 38.2%), and all-cause mortality (16.8% vs 15.6%). However, steeper declines were noted in KPNC than the United States among those aged 45 to 65 years for heart disease (48.3% KPNC vs 23.6% United States), coronary heart disease (55.6% vs 35.9%), stroke (55.8% vs 26.0%), and all-cause mortality (31.5% vs 9.1%). Sex-specific changes were generally similar. Despite significant declines in heart disease and stroke mortality, there remains an improvement gap nationally among those aged less than 65 years when compared with a large integrated healthcare delivery system. Interventions to improve cardiovascular mortality in the vulnerable middle-aged population may play a key role in closing this gap.